Coping with Heat Stress

Thursday, July 25, 2024

How Do Pigs Respond to Heat Stress & What Are the Consequences?

By Atta Kofi Agyekum, PHD

Heat stress is no longer an issue limited to tropical regions; countries in temperate regions are also experiencing hotter than usual summer months.

In Canada, the warm summer months increase the ambient temperature inside pig barns. When the ambient temperature within pig barns rises above 25 C, pigs will start to experience heat stress (Figure 1).

However, ambient temperature is not the only factor that causes heat stress; the relative humidity in the barn can also contribute, such that lower temperatures with high relative humidity can still have a large impact (Figure 1).

Why are pigs sensitive to heat stress?

Pigs do not sweat well. They have few sweat glands and their skin insulation impedes sensible heat loss, due to its thick subcutaneous fat depth. These factors, coupled with their high basal metabolic heat production and high lean tissue gain (due to intense genetic selection), make pigs particularly sensitive to heat stress, compared to other livestock animals.

How do pigs respond to heat stress and what are the consequences?

Pigs respond to heat stress through complex physiological and behavioural mechanisms, which have negative consequences for productive efficiency and health (Figure 2).

Heat-stressed pigs are less active and reduce their feed intake to reduce metabolic heat production and maintain body temperature. This reduction in feed intake results in reduced growth and feed efficiency. The physiological adjustments to heat stress can disturb the antioxidant status and cell function of the body, thereby compromising gut health, decreasing carcass value, and increasing morbidity and mortality. The negative impacts of heat stress on pigs ultimately impact farm profits. Heat stress is estimated to cost the U.S. swine industry more than half a billion U.S. dollars per year (the equivalent of approximately $680,000,000 Canadian; Pollman, 2010).

What can we do to help fattening pigs?

Fortunately, a variety of strategies can be employed to minimize the negative impact of heat stress during the summer months. These interventions can be grouped into environmental modifications, genetic selection, and nutritional strategies.

Several environmental and technical strategies can be employed to help fattening pigs cope with heat stress. These strategies mainly help by reducing or removing heat production and enhancing the pigs’ ability to lose heat. Examples include reducing stocking density, increasing air speed or ventilation rate, spraying fine water drops, barn ceiling and attic insulation, and unlimited access to fresh, clean drinking water. Genetic selection for heat-tolerant pigs may be another possible solution, but it still requires additional research to generate considerable information on its possible side effects on production traits.

Nutritional solutions for heat stress in fattening pigs

Nutritional strategies may present practical and cost-effective ways for managing the negative effects of heat stress on pig welfare and productivity. Various dietary and feeding approaches aim to reduce the thermic effect of feeding, maintain water and electrolyte balance, maintain nutrient intake, reduce oxidative stress, and improve gut health and function.

Reducing the dietary protein and/or fibre, using feed-grade amino acids, and increasing dietary fat can reduce the heat of feed digestion; your nutritionist can make these modifications. Increasing electrolyte intake should also be considered, due to the acid-base imbalance that occurs due to heat stress; this can be achieved by adding salt to feed or drinking water, providing extra sodium, potassium, and magnesium, and using oral rehydration therapies. The intake of dietary sources of antioxidants such as vitamin E, vitamin C, selenium, and polyphenols should be increased as the pig will not be able to produce enough antioxidants to meet its requirements during heat stress. It is also advisable to supplement fattening pigs with specific amino acids (e.g. betaine, glutamine) and minerals (e.g. zinc) that have immunomodulatory and anti-inflammatory effects to minimize “leaky gut” and promote gut health and function (Mayorga et al. 2019).

Betaine, a derivative of the amino acid glycine, is one of the most widely studied and commonly used supplements to mitigate heat stress in livestock animals because of its different functions at both the metabolic and gut levels. Betaine is also an organic osmolyte that can stimulate and maintain cellular osmolarity and function during heat stress. Betaine can be synthesized in the body through choline metabolism; however, during heat stress, the amount produced by the body will not be adequate to meet the animal’s requirements. Therefore, supplementing fattening pigs with betaine is one mitigation strategy to consider. Betaine can also be combined with antioxidant-rich feed additives to offer additional support.

In a recent research trial, fattening pigs experienced chronic mild to moderate heat stress (29 C) over two periods (days 10 to 42 and 85 to 106). The pigs fed betaine (Selko TNIbetain) and a plant-based antioxidant blend (Selko POmix flavour) across the growing period until slaughter showed a five-point improvement in feed efficiency, without significantly impacting costs (Table 1). This indicates that feed additives such as betaine and antioxidant-rich feed additives should be considered as practical solutions to help fattening pigs cope with heat stress during the hot summer months. BP